Method and apparatus for adaptive carrier allocation and power control in multi-carrier communication systems

ABSTRACT

An apparatus and process for allocating carriers in a multi-carrier system is described. In one embodiment, the process comprises determining a location (E, D, C, B, A; FIG.  6 ) of a subscriber ( 520 ) with respect to a base station ( 510 ), selecting carriers from a band of carriers to allocate to the subscriber ( 520 ) according to the location of the subscriber with respect to the base station ( 510 ), and allocating selected carriers to the subscriber ( 520 ).

FIELD OF THE INVENTION

The present invention relates to the field of multi-carriercommunication systems; more particularly, the present invention relatesto allocating carriers and performing power control in a multi-carriersystem.

BACKGROUND OF THE INVENTION

With high-speed wireless services increasingly in demand, there is aneed for more throughput per bandwidth to accommodate more subscriberswith higher data rates while retaining a guaranteed quality of service(QoS). In point-to-point communications, the achievable data ratebetween a transmitter and a receiver is constrained by the availablebandwidth, propagation channel conditions, as well as thenoise-plus-interference levels at the receiver. For wireless networkswhere a base-station communicates with multiple subscribers, the networkcapacity also depends on the way the spectral resource is partitionedand the channel conditions and noise-plus-interference levels of allsubscribers. In current state-of-the-art, multiple-access protocols,e.g., time-division multiple access (TDMA), frequency-divisionmultiple-access (FDMA), code-division multiple-access (CDMA), are usedto distribute the available spectrum among subscribers according tosubscribers' data rate requirements. Other critical limiting factors,such as the channel fading conditions, interference levels, and QoSrequirements, are ignored in general.

Recently, there is an increasing interest in orthogonalfrequency-division multiplexing (OFDM) based frequency division multipleaccess (OFDMA) wireless networks. One of the biggest advantages of anOFDM modem is the ability to allocate power and rate optimally amongnarrowband sub-carriers. OFDMA allows for multi-access capability toserve increasing number of subscribers. In OFDMA, one or a cluster OFDMsub-carriers defines a “traffic channel”, and different subscribersaccess to the base-station simultaneously by using different trafficchannels.

Existing approaches for wireless traffic channel assignment aresubscriber-initiated and single-subscriber (point-to-point) in nature.Since the total throughput of a multiple-access network depends on thechannel fading profiles, noise-plus-interference levels, and in the caseof spatially separately transceivers, the spatial channelcharacteristics, of all active subscribers, distributed orsubscriber-based channel loading approaches as fundamentallysub-optimum. Furthermore, subscriber-initiated loading algorithms areproblematic when multiple transceivers are employed as the base-station,since the signal-to-noise-plus-interference ratio (SINR) measured basedon an omni-directional sounding signal does not reveal the actualquality of a particular traffic channel with spatial processing gain. Inother words, a “bad” traffic channel measured at the subscriber based onthe omni-directional sounding signal may very well be a “good” channelwith proper spatial beamforming from the base-station. For these tworeasons, innovative information exchange mechanisms and channelassignment and loading protocols that account for the (spatial) channelconditions of all accessing subscribers, as well as their QoSrequirements, are highly desirable. Such “spatial-channel-and-QoS-aware”allocation schemes can considerably increase the spectral efficiency andhence data throughput in a given bandwidth. Thus, distributedapproaches, i.e., subscriber-initiated assignment are thus fundamentallysub-optimum.

Linear Modulation Techniques, such as Quadrature phase shift keying(QPSK), Quadrature Amplitude Modulation (QAM) and multi-carrierconfigurations provide good spectral efficiency, however the modulatedRF signal resulting from these methods have a fluctuating envelope. Thisputs stringent and conflicting requirements on the power amplifier (PA)used for transmitting communications. A fluctuating envelope of themodulating signal requires highly linear power amplification. But inorder to achieve higher efficiency and improve uplink budget, poweramplifiers have to operate close to compression and deliver maximumpossible power. As a result, there is a trade off for power versusamount of nonlinear amplification a system can handle.

Furthermore, non-linearity in the PA generates intermodulationdistortion (IMD) products. Most of the IMD products appear asinterference to adjacent channels. This power is referred to AdjacentChannel Leakage Power Ratio (ACPR or ACLR) in wireless standards.

The ACPR is important to the FCC and wireless standards because of theco-existence with other users of the spectrum operating in adjacent andalternate channels. In band or channel distortion affects theperformance of the licensee's own spectrum, which, in turn, affects thetransmitter signal-to-noise ratio (SNR) of other users in the samesystem.

RF link budget in a wireless communication system refers to balancingthe available transmit power, antenna gain, propagation loss anddetermining maximum allowable distance at which received power meets aminimum detectable signal threshold. Several parameters influence the RFlink budget. Two main factors, transmitter RF power available from thePA and receiver sensitivity, are under circuit designer's control. Basestation design has relatively more degree of freedom than the CustomerEquipment (CE). This results in the RF link budget being imbalanced inthe uplink: This limitation is hard to overcome given the cost, size andbattery life requirements of CE.

SUMMARY OF THE INVENTION

An apparatus and process for allocating carriers in a multi-carriersystem is described. In one embodiment, the process comprisesdetermining a location of a subscriber with respect to a base station,selecting carriers from a band of multiple carriers to allocate to thesubscriber according to the location of the subscriber with respect tothe base station, allocating selected carriers to the subscriber, andindicating to the subscriber whether or not to adjust transmit powerabove its normal transmit power range.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the invention, which, however, should not be taken tolimit the invention to the specific embodiments, but are for explanationand understanding only.

FIG. 1A illustrates a multi-carrier system.

FIG. 1B illustrates spectral re-growth in a multi-carrier system.

FIG. 1C illustrates power amplifier operating regions.

FIG. 2 is a flow diagram of one embodiment of a process for allocatingcarriers in a multi-carrier system.

FIG. 3 is a flow diagram of one embodiment of a process for a basestation to allocate carriers in a multi-carrier system.

FIG. 4 is a flow diagram of one embodiment of a process by which asubscriber unit is allocated carriers in a multi-carrier system.

FIG. 5 illustrates an exemplary system having a base station and asubscriber unit.

FIG. 6 illustrates a system having a base station and multiplesubscribers grouping based on constant path loss contours.

FIG. 7 illustrates an exemplary WCDMA modulation terminal power outputfor a 45 dBc ACLR.

FIG. 8 illustrates an exemplary WCDMA modulation terminal power outputfor a 33 dBc ACLR as defined by the 3GPP standard.

FIG. 9 illustrates an OFDM selective tone modulation terminal poweroutput.

FIG. 10 illustrates NPR due to operating a Customer Equipment (CE) at anincreased power level.

FIG. 11 is a block diagram of one embodiment of a customer equipmenttransmitter.

FIG. 12 is a block diagram of one embodiment of a base transmitter.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

A carrier allocation technique for use in multi-carrier systems isdescribed. The carrier allocation technique selects carriers, orsubcarriers, of a band to allocate to a subscriber or Customer Equipment(CE) for their use. In one embodiment, the allocation is performed suchthat carriers closer to or at the center of the band are allocated tosubscriber units and CEs further away from a base station and carrierscloser to the edge of the band are allocated to those CEs and subscriberunits closer to the base station.

In one embodiment, the technique described herein increases thetransmitter radio frequency (RF) power available from a power amplifier(PA) of the CPE, CE, terminal, subscriber unit, portable device, ormobile by exploiting the multi-carrier nature of multiple carriersystems, such as, for example, an orthogonal frequency-division multipleaccess (OFDM) system. This technique may double or even quadruple the PAoutput power, resulting in balancing RF link design in a two-waycommunication system. In one embodiment, this technique may be employedto control a PA device to operate at a higher power and simultaneouslymeet the Adjacent Channel Leakage Power (ACPR) emission requirementsassociated with a standard (to which the system is adhering). This mayoccur when a subscriber unit's power control drives up the transmitpower when farther away from the base station after being allocatedcarriers at or near the center of the band being allocated. Thus, thetechnique described herein allows the transmit power to be driven up ordown based on the position of the subscriber. In one embodiment, theselective carrier method described herein results in 3 to 6 dB increasedpower, which can considerably improve RF link budget.

Such a method of allocation can be used in a wireless system employingfixed, portable, mobile subscribers or a mixture of these types ofsubscribers. Note that the term “subscriber,” “customer equipment” and“subscriber unit” will be used interchangeably.

In the following description, numerous details are set forth to providea thorough understanding of the present invention. It will be apparent,however, to one skilled in the art, that the present invention may bepracticed without these specific details. In other instances, well-knownstructures and devices are shown in block diagram form, rather than indetail, in order to avoid obscuring the present invention.

Some portions of the detailed descriptions that follow are presented interms of algorithms and symbolic representations of operations on databits within a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The present invention also relates to apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but is not limited to, any type ofdisk including floppy disks, optical disks, CD-ROMs, andmagnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any typeof media suitable for storing electronic instructions, and each coupledto a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the invention as described herein.

A machine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium includes read onlymemory (“ROM”); random access memory (“RAM”); magnetic disk storagemedia; optical storage media; flash memory devices; electrical, optical,acoustical or other form of propagated signals (e.g., carrier waves,infrared signals, digital signals, etc.); etc.

Selective Carrier Allocation

The selective carrier allocation technique disclosed is applicable tomulti-carrier systems. Example of these include Orthogonal FrequencyDivision Multiple Access (OFDMA), multi-carrier CDMA, etc. As anexample, the selective carrier allocation will be described below withreference to an OFDM system.

In an OFDM system, OFDMA is used for uplink communications to share thespectrum with co-users of the same sector. In other words, thesubscriber or CE uses only a portion of the available carriers (ormulti-tones) for any given transmission. The base station allocatesthese carriers to subscribers in a methodical way to avoid interfering,to the extent possibly, with other users in the same sector. Thedecision to select a set of carriers can be based on several criteriasuch as, for example, but not limited to, fading, signal-to-noise ratio(SNR) and interference.

FIG. 1A illustrates the spectrum of one embodiment of a multi-carriersystem such as OFDM. In such a system, there are a number of modulatedcarriers (n) occupying a certain bandwidth. For a 3GPP system, thisbandwidth is 3.84 MHZ. Non-linearities within the PA mixes or modulatesthese tones with each other to generate intermodulation distortion (IMD)products. A dominant element of these IMDs is due to third order (2f×f)and fifth order (3f×2f) mixing. The IMD generated by a wide bandmultiple tone signal causes the spectrum to spread energy (or spill)beyond the allocated 3.84 MHz bandwidth. This is commonly referred asspectral re-growth. FIG. 1B depicts the spectral re-growth phenomena.

Spectral re-growth due to third order mixing falls in the upper andlower adjacent channels, whereas the fifth order mixing product falls onthe upper and lower alternate channels. Other higher order products areusually weaker and can be ignored for most practical applications.

As mentioned above, non-linearities in the PA are rich in third orderproducts and are of most concern. These products are seen in theadjacent channels as ACLR power. The fifth and higher order products arespread out further from the main channel and their effect is not adeterminant factor.

In a multi-carrier wireless system using ‘N’ tones, the subscriber unitor CE uses only a limited number of tones, such as ‘X’ tones where X isa much smaller number compared to N. A CE or subscriber unit using acluster of X tones will occupy (X/N) of the total channel bandwidth. Asdepicted in FIG. 1B, spectral re-growth due to third and fifth orderproducts is stronger and is very important. These determine the adjacentand alternate channel coupled powers.

If clusters around the center of the allocated channel are chosen fortransmission, then it is possible for the main IMD products to fallwithin the channel bandwidth. As a consequence, these carriers canwithstand higher level of non-linear amplification and can be used totransmit at increased power levels compared to other carriers. TheCEs/subscriber units closer to the base station operate at lower powerthan the CEs/subscriber units farther away. FIG. 1C depicts the linearoperation and IMD products generated as a function of operating power.

CEs/subscriber units farther away from the base encounter larger pathloss and they need to operate at a higher power. Operating at higherpower produces a higher level of IMD products and causes spectralgrowth. These CEs/subscriber units can be allocated the clusters aroundthe center of the operating channel, thereby reducing, and potentiallyminimizing, the spill over to adjacent channels while simultaneouslyachieving higher transmit power.

FIG. 2 illustrates one embodiment of a process for allocating carriersin a multi-carrier system. The process is performed by processing logicthat may comprise hardware (e.g., circuitry, dedicated logic, etc.),software (such as is run on a general purpose computer system or adedicated machine), or a combination of both.

Referring to FIG. 2, the process begins with processing logic of a basestation comparing interference to adjacent channels (e.g., adjacentchannel leakage power) with the output power of a subscriber unit in amulti-carrier system as a function of distance of the subscriber unitfrom the base station (processing block 201). Then the processing logicof the base station selectively allocates one or more carriers to thesubscriber unit based on results of the comparison (processing block202). In one embodiment, one or more subscribers closer to the basestation are allocated carriers closer to the band edges of the operatingchannel and one or more subscribers farther from the base station areallocated carriers around the center of the operating channel. Referringto FIG. 1B, the CE occupies main channel bandwidth of [(X/N)*3.84] Mhzfor uplink transmission. Third order IMD products generated by thischannel will occupy [(X/N)*3.84]Mhz on the upper and lower sides of themain channel. Similarly, fifth order IMD products will occupy another[(X/N)*3.84]Mhz on either side of the third order products. Thus, twicethe main channel bandwidth on each side of the main channel will beoccupied by significant components of IMD. Therefore, the clustersfalling within {½[3.84−(4*main channel bandwidth)]} from the center ofthe band can benefit due to this carrier allocation method.

As a result of this allocation, dominant undesired spectral re-growthscan be restricted to lie within the wireless system's occupied channeland avoid interference to adjacent channels. Furthermore, the PA of asubscriber unit can be operated closer to 1 dB compression point anddeliver higher power than the conventional usage. Operation nearcompression point also improves the PA efficiency.

In one embodiment, the carriers being allocated are orthogonalfrequency-division multiple access (OFDMA) carriers. The OFDMA carriersmay be allocated in clusters. In another embodiment, each carrier may bea spreading code and the multi-carrier system comprises a multi-carriercode-division multiple-access (MC-CDMA) system.

In one embodiment, the multi-carrier system is a wireless communicationsystem. Alternatively, the multi-carrier system is a cable system.

FIG. 3 illustrates one embodiment of a process performed by a basestation for allocating carriers of a band in a multi-carrier system. Theprocess is performed by processing logic that may comprise hardware(e.g., circuitry, dedicated logic, etc.), software (such as is run on ageneral purpose computer system or a dedicated machine), or acombination of both.

Referring to FIG. 3, the process begins with processing logic receivinga communication indicating that a subscriber intends to transmit(processing block 301). In one embodiment, the communication is a randomaccess intention to transmit sent by the subscriber and is received by abase.

In response to receiving the communication, processing logic of the basecalculates the transmit power requirements for the subscriber unit anddetermines whether the subscriber is near or far (processing block 302).In one embodiment, the processing logic calculates the time delay andpath loss associated with the subscriber and uses this information tocalculate the transmit power requirements. Note that transmit power isbased on the path loss, and the time delay provides additionalinformation on the distance of the customer equipment. In oneembodiment, processing logic uses additional factors such as, forexample, SINR, in calculating the transmit power requirements

Based on the transmit power requirements calculated and thedetermination of whether the subscriber unit is near or far, processinglogic allocates carriers to the subscriber (processing block 303). Inone embodiment, each carrier is identified by a tone number or a groupof carriers are identified by a cluster number in a multi-carriersystem. The base instructs the customer equipment to use a particularset of carriers identified by their number. In one embodiment, theprocessing logic in the base station allocates carriers near the centerof the band (it is to allocate) to subscriber units far away from thebase station and carriers near the edges of the band to subscriber unitscloser to the base station. The processing logic may attempt to allocatemore carriers closer the edges of band in order to save carriers forcurrently non-present subscriber units that will enter the coverage areaof the base station in the future or present subscriber units that willmove from a location close to the base station to one farther away fromthe base station.

In one embodiment, in order to allocate carriers to subscribers,processing logic in the base station assigns a priority code to eachsubscriber unit based on the location of the subscriber unit in relationto the base station (e.g., whether the subscriber unit is far away fromor near to the base station). A priority code is assigned based on thetransmit power requirement, which, in turn, is based on the path loss.The location of the CE determines the path loss. In general, the fartheraway the CE from the base, the path loss is more, but not always. Forexample, there could be a nearby CE (to the base) but behind a tallbuilding or hill, causing an RF shadow. In such a case, this CE willhave large path loss. In one embodiment, the subscriber farthest fromthe base station is allocated priority code #1, followed by the nextfarthest subscriber with priority code #2, and so on.

Processing logic in the base station may also send a command to asubscriber unit to cause the subscriber unit to use either a normal orextended power control range of “z dB” above the normal range dependingon priority and carrier allocation (processing block 304). In otherwords, the base station sends commands to the subscriber to indicatewhether to raise or lower its transmit power. This is closed loop powercontrol to tune the transmit power of the subscriber.

In one embodiment, processing logic in the base station also adjustspower control setting for the subscriber in a closed loop power controlsetting and continuously monitors received power from subscribers(processing block 305). For example, if the channel characteristicschange, the path loss changes and the base has to update the transmitpower of the CE.

FIG. 4 illustrates one embodiment of a process performed by a subscriberunit in a multi-carrier system. The process is performed by processinglogic that may comprise hardware (e.g., circuitry, dedicated logic,etc.), software (such as is run on a general purpose computer system ora dedicated machine), or a combination of both.

Referring to FIG. 4, processing logic in the subscriber unit sends acommunication to a base station to indicate that it intends to transmit(processing block 401). In one embodiment, the processing logic sends arandom access intention to transmit.

Processing logic in the subscriber unit receives an indication of anallocation of carriers based on the location of the subscriber unit withrespect to a base station (processing block 402). In one embodiment, theindication comes from the base station on the control channel.

In one embodiment, processing logic in the subscriber unit also receivesa command from the base station to use either a normal or extended powercontrol range (processing block 403). In one embodiment, whether thebase station indicates to the subscriber unit to use the normal orextended power control range is based on assigned priority and carrierallocation. These command indicate to the subscriber unit that it is todrive up or reduce its transmit power, and whether it is one or theother depends on the position of the subscriber relative to the basestation.

FIG. 5 is a block diagram of one embodiment of a typical system.Referring to FIG. 5, a base 510 is shown communicably coupled to asubscriber unit 520. Base station 510 includes a power control unit 511coupled to a carrier allocator 512. Carrier allocator 512 allocatescarriers of a band to subscriber units, such as subscriber unit 520, inthe system, and power control unit 511. In one embodiment, carrierallocator 512 includes a priority code look up table (LUT) 513. At agiven instant, the farthest subscriber(s) may not be active in thesystem. Therefore, the embodiment described here uses predeterminedthreshold limits in the LUT to determine the carrier allocation andpower control.

In one embodiment, carrier allocator 512 decides the spectral prioritybased on the information gathered from the access requests sent bysubscriber units. Carrier allocator 512 assigns priorities to eachsubscriber based on location with respect to base station 510 and thenallocates carriers to each subscriber. Carrier allocator 512 allocatescarriers at or near the center of the band to the subscribers farthestaway from base station and allocates carriers closer to or at the edgeof the band to subscribers closest to base station 510. In oneembodiment, carrier allocator 512 attempts to allocate sub-carriers atthe edges of the band to the nearest subscribers and make room forpotential subscribers located farther way from base station 510.

In one embodiment, carrier allocator 512 classifies subscribers intopriority groups rather than assigning them individual priorities. In acell-based system, carrier allocator 512 identifies subscribers near thecenter of the sector form one group and have a certain priority code. Ifconstant path loss contours are imagined, subscribers falling betweencertain path losses or between these contours form a group and areassigned a certain priority.

Carrier allocator 512 also continuously monitors the allocation of thecarriers used by various subscribers in the system and dynamicallyreallocates the carriers to subscribers. For example, in a mobilesystem, both the mobile unit(s) and base station continuously monitorthe path loss and may perform reallocation and adaptive power control toextend the range. If the subscriber has moved closer to the basestation, then carrier allocator 512 changes the priority codes anddeallocates the sub-carriers near the center for other potentialsubscribers. Similarly, when a subscriber moves away from base station510, then carrier allocator changes the priority codes and allocates thesub-carriers near the center of the band depending on availability.

The priority determined by sub-carrier allocator 512 is communicated tosubscriber unit 520 by power control unit 511. In one embodiment,sub-carrier allocator 512 transmits information about the specificcarriers available for the subscriber, the priority code on thesecarriers, and the power control range (normal or extended). Thiscommunication indicates to the subscribers to use a certain powercontrol range based on their priority and carrier allocation. Powercontrol unit 511 indicates to subscriber unit 520 the transmit powerlevel it is to use. In one embodiment, power control unit 511 indicatesto subscriber unit 520 to extend power control range if subscriber unit520 is allocated carriers at center of the spectrum. That is, powercontrol unit 511 sends out power control commands to the subscribers inorder for the received power at base station 510 to be at the desiredlevel. Thus, power control unit 511 is responsible for closed loop powercontrol.

Subscriber unit 520 includes a power control unit 521. Power controlunit 521 controls the transmit power of subscriber unit 520. That is,power control unit 521 adjusts the transmit power from subscriber unit520 to keep the received power at base station 510 at a predeterminedlevel desired by base station 510. Thus, power control unit 521 isresponsible for closed loop power control.

In one embodiment, power control unit 521 processes power controlcommands received from the base station and determines the allocatedpower control range for subscriber unit 520. In one embodiment, powercontrol unit 521 includes a normal power control range (i to j) and anextended power control range (m to n) and power control unit 521 tellssubscriber unit 520 to extend the power control range if the subscriberis allocated sub-carriers at the center of the spectrum. In oneembodiment, the power control unit signals the gain control circuit ofthe transmitter of the subscriber unit to extend the power controlrange. In one embodiment, subscriber unit 520 is responsive to a codereceived from the base station which indicates the power control rangeto use. Subscriber unit 520 may include a look up table (LUT) thatstores power control ranges and/or transmit powers associated with eachcode received from the base station, and uses the code as an index intothe LUT to determine what power control range and/or transmit power isbeing requested.

The system maintains its ACLR, however by allocating carriers near or atthe center of the band, the subscriber gets an increase of power (e.g.,3-6 db). That is, in a system with subscribers typically transmitting at17 dbm with a 3 kilometer range, a subscriber allocated carriers at thecneter may be able to transmit 18 or 19 dbm, thereby allowing it toextend its range potentially to 4 km.

FIG. 11 is a block diagram of one embodiment of a customer equipmenttransmitter. Referring to FIG. 11, an upconverter 1101 mixes a signal tobe transmitted with a signal from a local oscillator 1102 to create anupconverted signal. The upconverted signal is filtered by filter 1103.The filtered signal output from filter 1103 are input to a variable gainamplifier 1104, which amplifies the filtered signal. The amplifiedsignal output from variable gain amplifier 1104 is mixed with a signalfrom a local oscillator 1106 using upconverter 1105. The upconvertedsignal output from upconverter 1105 is filtered by filter 1107 and inputto variable gain amplifier 1108.

Variable gain amplifier 1108 amplifies the signal output from filter1107 based on a control signal. Variable gain amplifier 1108 and thecontrol signal is controlled by DSP engine 1109 which executes a powercontrol algorithm 1121 with the use of priority code and power controlrange look-up table (LUT) 1122. Both the power control algorithm 1121and priority code and power control range LUT 1122 are stored inexternal memory. In addition, memory 1120 is also coupled to DSP engine1109. In one embodiment, when power is turned off power controlalgorithm 1121 and LUT 1122 are stored in external memory 1120. DSPengine 1109 is also coupled to external memory 1120 so that it candownload code to the internal memory of DSP engine 1109. The output ofDSP engine 1109 is control signal that is input to FPGA/ASIC 1111, whichbuffers the output data from DSP engine 1109 and formats it so that thedata is readable by digital-to-analog (D/A) converter 1110. The outputof ASIC 1111 is coupled to an input of D/A converter 1110 which convertsthe control signal from digital-to-analog. The analog signal is input tovariable gain amplifier 1108 to control the gain that is applied tooutput of filter 1107.

The amplified signal output from output variable gain amplifier 1108 isinput to a power amplifier 1130. The output of power amplifier 1130 iscoupled to a duplexer or transmit switch 1131. The output duplexer/TRswitch 1131 is coupled to antenna 1140 for transmission therefrom.

FIG. 12 is a block diagram of one embodiment of a base transmitter.Referring to FIG. 12, DSP engine 1209 performs power control andsubcarrier allocation using power control algorithm 1221 in conjunctionwith a priority code and power control range look-up table 1222 (storedin memory), and subcarrier allocator 1240, respectively. In addition,memory 1220 is also coupled to DSP engine 1209. The output of DSP engine1209 is power control information that is embedded into a transmitmessage as control bits. The transmit message is input to FPGA/ASIC1211, which buffers the output data from DSP engine 1209 and formats itso that the data is readable by D/A converter 1210. The output of ASIC1211 is input to modem and D/A converter 1210 which modulates the signaland converts the signal from digital to analog. The analog signal isinput to upconverter 1201.

Upconverter 1201 mixes the signal from converter 1210 with a signal froma local oscillator 1202 to create an upconverted signal. The upconvertedsignal is filtered to filter 1203. The filter signals output to avariable gain amplifier 1204 which amplifies the signal. The amplifiedsignal is output from variable gain amplifier 1204 and mix with a signalfrom a local oscillator 1206 using upconverter 1205. The upconvertedsignal output from upconverter 1205 is filtered by 1207.

Variable gain amplifier 1208 amplifies the signal output from filter1207. The amplified signal output from variable gain amplifier 1208 isinput to a power amplifier 1230. The output of power amplifier 1230 iscoupled to a duplexer or transmit switch 1231. The output duplexer/TRswitch 1231 is coupled to antenna 1240 for transmission therefrom.

An Exemplary System

FIG. 6 illustrates an exemplary system having a base station, with itscoverage area, and multiple subscribers. The coverage range of the basestation is divided into distance groups 1 to 4. Although not limited assuch, there are 5 subscribers A, B, C, D and E sending random accessintention to transmit. These subscribers are located physically asdepicted in FIG. 6.

The spectrum has been divided into sub groups numbered 1, 2, 3 and 4.Grouping is based on path loss in this case. Table 1 summarizes thegroup attributes and transmit power requirements of each subscriberunit. TABLE 1 Grouping and Power Control table Terminal TransmitSpectral Group Path loss power in Priority Spectrum number in dB dBmCode Allocation Power Control Range 1 >−100 <−13 4 Center +3 Normal −40dBm to +17 dBm 2 −101 to −115 −12 to +2 3 Center +2 Normal −40 dBm to+17 dBm 3 −116 to −130 +3 to +17 2 Center +1 Normal −40 dBm to +17 dBm 4−131 to −136 +18 to +23 1 Center Extended −40 dBm to +23 dBm

The allocation process to allocate carriers to subscriber A is asfollows. First, subscriber A sends a random access intention to transmitto the base station. Second, the base station receives the request andcalculates time delay and path loss for subscriber A. Next, based onresults of the calculation of the time delay and the path loss forsubscriber A and Table 1, the base station determines that subscriber Abelongs to distance group-4. The base station also determines thatsubscriber A needs to transmit with spectral priority code-1. Then thebase station commands to use an extended power control range andallocates carriers in the center of the spectrum. Thereafter, the basestation and subscriber A adjust power control settings in a closed looppower control mode and continuously monitor. In the case of the basestation, the base station continuously monitors the signals receivedfrom subscribers (and calculates the time delay and path loss).

It should be noted that subscribers may or may not be allocated carriersthat are closer to the edge or to the center of the band in comparisonto a subscriber that is adjacent to them. For example, in the case ofFIG. 6, in one allocation, subscriber E could be allocated carriersclosest to the edges of a band, followed by carriers allocated tosubscriber D being the next closest, followed by carriers allocated tosubscriber C, and so on, until subscriber A, which would be allocatedcarriers closest to the center of the band (in comparison to subscribersB-E). However, during other allocations, one or more subscribers may beallocated carriers closer to the edge of the band or closer to thecenter of the band than carriers allocated to a subscriber who is closerto or further from the base station, respectively. For example, in FIG.6, it is possible that subscriber D is allocated carriers closer to theedge of the band than those allocated to subscriber E.

Comparison with a Prior Art System

FIG. 7 is a spectral plot for ACLR of 45 dBc for a system having ahardware platform designed for a 1800 MHZ TDD wireless communicationsystem. The 45 dBc amount is selected because if a system is designed tocoexist with ANSI-95, ACLR of 45 dBc has to be met, and ACLR for a PCSCDMA system is defined in ANSI-95 to be 45 dBc in a RBW of 30 KHz. Inorder to meet the ACLR of 45 dB, the output power capability of theterminal is about +17 dbM.

FIG. 9 shows the capability of terminal operating with the use of thecarrier allocation described herein is +23 dBm for ACLR of 33 dBc. Oneof the evolving standards, 3GPP, defines the ACLR to be 33 dBc for CEs.

Note that operating the PA of a subscriber closer to compression formore power results in in-band distortion. However, employing themethodology of the present invention does not degrade the systemperformance. This fact may be shown through the use of an example asgiven below.

Power control algorithms ensure that power received at the base stationfrom all CEs or subscribers arrive at the same level. This means thatthe signal peak to average ratio received at the base is near zero. Itis assumed in this example that a cluster of carriers is allocated atthe center of the channel to the farthest user and this user meets thetransmit signal quality and SNR requirements for the base receiver todemodulate. If the minimum detectable signal at the receiver is −92 dBmfor an SNR of 10 dB, then the receive noise floor is set at −102 dBm. Ifthe farthest CE operates at a TX SNR of 12 dB or better and powercontrol algorithm sets the system such that this signal from the CEarrives at −92 dBm to the base, then the IMD products generated by thisCE are buried in the RX noise floor. All the other channels see only thereceive noise floor. The receiver thermal noise floor is inherent to allcommunication system. Hence, the overall performance of the system hasnot been degraded.

In order to increase, and potentially maximize, the output poweravailable to the farthest terminal, a cluster at the center of thechannel can be allocated. This way the IMD products and spectralre-growth generated by the farthest user does not cause spill over tothe adjacent channel.

FIG. 9 shows that the terminal is capable of transmitting at outputpower level of +25 dBm while maintaining ACLR of 45 dBc. This is animprovement of nearly 8 dB compared to situation described above in FIG.7. As mentioned above, the PA efficiency is better when it operatescloser to its saturated power. Thus, it improves the battery life at nocost to hardware implementation. Resulting inter modulation products forthe in band channel are measured to be 14 dB. This distortion productpower level is lower than the receiver SNR requirement of 12 dBrequirement for the up link in other systems.

In band Noise Power Ratio (NPR) typically characterizes distortion formulti-carrier system. FIG. 10 is a measurement of NPR when the CE isoperated at a power level of +23 dBm. NPR is about 22 dB, therebyindicating the distortion levels will be buried well below the thermalnoise floor of the base station receiver.

Table 2 below summarizes the performance improvements achieved by theselective carrier allocation method described herein. TABLE 2Performance Comparison Channel Power NPR ACPR conventional ACPR -Selective carrier (dBm) (dB) way allocation method 14 32 >45 >45 17 3245 >45 20 28 39 >45 23 22 33 >45 24 18 — >45 25 12 — >45 26 9 — 45

CONCLUSION

A carrier allocation method and apparatus are described whichpotentially maximizes the subscriber unit or customer equipment CEtransmitter power. In one embodiments improvements from 3 dB to 6 dB canbe achieved using the methodology described herein to allocate OFDMtones to subscriber units or CEs.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that anyparticular embodiment shown and described by way of illustration is inno way intended to be considered limiting. Therefore, references todetails of various embodiments are not intended to limit the scope ofthe claims which in themselves recite only those features regarded asessential to the invention.

1. A process for allocating carriers in a multicarrier system, theprocess comprising: determining a location of a subscriber with respectto a base station; selecting carriers from a band of multi-carriers toallocate to the subscriber according to the location of the subscriberwith respect to the base station; allocating selected carriers to thesubscriber, and indicating to the subscriber whether or not to adjusttransmit power to above its normal transmit power range.
 2. The processdefined in claim 1 wherein the closer the subscriber is to the basestation the farther away the selected carriers are from the center ofthe band.
 3. The process defined in claim 1 wherein selecting carriersfrom the band of multi-carriers comprises: selecting carriers closer toor at the center of the band when the subscriber is far away from thebase station; and selecting carriers farther away from the center of theband when the subscriber is close to the base station.
 4. The processdefined in claim 1 further comprising: receiving a request from asubscriber; calculating a time delay and a path loss associated with thesubscriber; and determining transmit power requirements for thesubscriber based on the time delay and the path loss.
 5. The processdefined in claim 4 wherein determining transmit power requirements isfurther based on signal-to-noise-plus-interference ratio.
 6. The processdefined in claim 1 further comprising sending a command to thesubscriber to use either a normal or extended power control range basedon carrier allocation.
 7. The process defined in claim 6 furthercomprising adjusting a power control setting for the subscriber at thebase station.
 8. The process defined by claim 7 further comprising:assigning a spectral priority code to the subscriber based on whetherthe subscriber is near to or far from the base station, and whereincarrier allocation occurs based on the spectral priority code.
 9. Theprocess defined in claim 8 further comprising allocating carriers at thecenter of the band to the subscriber when the subscriber is assigned afirst predetermined spectral priority code.
 10. The process defined inclaim 9 further comprising allocating carriers adjacent to carriers atthe center of the band to the subscriber when the subscriber is assigneda second predetermined spectral priority code that is of a lowerpriority than the first predetermined spectral priority code.
 11. Anapparatus comprising: a carrier allocator to determine spectral prioritybased on information gathered from access requests sent by subscriberunits; and a power control unit coupled to the carrier allocator toindicate a power control range for each of the subscriber units.
 12. Theapparatus defined in claim 11 wherein the carrier allocator allocatescarriers at edges of a band to the nearest subscribers.
 13. Theapparatus defined in claim 11 wherein the carrier allocator classifiessubscribers into priority groups and allocates carriers to each of thesubscribers based on the priority group in which each of the subscribersresides.
 14. The apparatus defined in claim 11 wherein the carrierallocator monitors allocation of the carriers and dynamicallyreallocates carriers to subscribers.
 15. The apparatus defined in claim14 wherein the carrier allocator reallocates carriers closer to thecenter of the band when a subscriber moves farther away from the basestation.
 16. The apparatus defined in claim 14 wherein the carrierallocator reallocates carriers farther from the center of the band whena subscriber moves closer to the base station.
 17. The apparatus definedin claim 11 wherein the power control units commands at least one of thesubscriber units to extend the power control range of the subscriber.18. A method comprising: a subscriber sending an indication to transmit;and the subscriber receiving an indication of carriers selected based ondistance of the subscriber from the base station in relation to othersubscribers, the carriers for use in communicating with a base station.19. The method defined in claim 18 further comprising driving up or downsubscriber transmit power depending on a location of the subscriber inrelation to a base station.
 20. The method defined in claim 19 furthercomprising: receiving a power control command from the base station, andwherein the subscriber drives up or down the subscriber transmit powerbase on
 21. The method defined in claim 18 further comprising: receivinga command to use either a normal or extended power control range basedon the carriers allocated; and transmitting at a higher power whilesimultaneously meeting FCC ACPR emission requirements.
 22. A method forcommunicating between a base station and subscribers comprising:comparing interference to adjacent channel leakage power with outputpower of a subscriber; selectively allocating one or more carriers of aband to a subscribers in a multi-carrier system based on results ofcomparing the adjacent channel leakage power to the output power,wherein one or more subscribers closer to a base station are allocatedcarriers closer to the band edges of the operating channel and one ormore subscribers further from the base station are allocated carriersnear or at the center of the operating channel.
 23. The method definedin claim 22 wherein the adjacent channel leakage power the FCC AdjacentChannel Leakage Power (ACPR).
 24. The method defined in claim 22 whereinthe carriers being allocated comprise orthogonal frequency-divisionmultiple access (OFDMA) carriers.
 25. The method defined in claim 22wherein each carrier being allocated comprise a cluster of orthogonalfrequency-division multiple access (OFDMA) carriers.
 26. The methoddefined in claim 22 wherein at least one of the one or more carrierscomprises a spreading code and the multi-carrier system comprises acode-division multiple-access (CDMA) system.
 27. The method defined inclaim 22 wherein at least one of the one or more carriers comprises anantenna beam in a space-division multiple access (SDMA) system.
 28. Themethod defined in claim 22 wherein the multi-carrier system comprises awireless system.
 29. The method defined in claim 22 wherein themulti-carrier system comprises a cable system.